Can you bring yourself to have one fewer of these?
Photograph: fStop Images GmbH/Alamy

The greatest impact individuals can have in fighting climate change is to have one fewer child, according to a new study that identifies the most effective ways people can cut their carbon emissions.

The next best actions are selling your car, avoiding long flights, and eating a vegetarian diet. These reduce emissions many times more than common green activities, such as recycling, using low energy light bulbs or drying washing on a line. However, the high impact actions are rarely mentioned in government advice and school textbooks, researchers found.

Carbon emissions must fall to two tonnes of CO2 per person by 2050 to avoid severe global warming, but in the US and Australia emissions are currently 16 tonnes per person and in the UK seven tonnes. “That’s obviously a really big change and we wanted to show that individuals have an opportunity to be a part of that,” said Kimberly Nicholas, at Lund University in Sweden and one of the research team.

The new study, published in Environmental Research Letters, sets out the impact of different actions on a comparable basis. By far the biggest ultimate impact is having one fewer child, which the researchers calculated equated to a reduction of 58 tonnes of CO2 for each year of a parent’s life.

The figure was calculated by totting up the emissions of the child and all their descendants, then dividing this total by the parent’s lifespan. Each parent was ascribed 50% of the child’s emissions, 25% of their grandchildren’s emissions and so on.

“We recognise these are deeply personal choices. But we can’t ignore the climate effect our lifestyle actually has,” said Nicholas. “It is our job as scientists to honestly report the data. Like a doctor who sees the patient is in poor health and might not like the message ‘smoking is bad for you’, we are forced to confront the fact that current emission levels are really bad for the planet and human society.”

“In life, there are many values on which people make decisions and carbon is only one of them,” she added. “I don’t have children, but it is a choice I am considering and discussing with my fiance. Because we care so much about climate change that will certainly be one factor we consider in the decision, but it won’t be the only one.”

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Overpopulation has been a controversial factor in the climate change debate, with some pointing out that an American is responsible for 40 times the emissions produced by a Bangladeshi and that overconsumption is the crucial issue. The new research comes a day after researchers blamed overpopulation and overconsumption on the “biological annihilation” of wildlife which has started a mass extinction of species on the planet.

Nicholas said that many of the choices had positive effects as well, such as a healthier diet, as meat consumption in developed countries is about five times higher than recommended by health authorities. Cleaner transport also cuts air pollution, and walking and cycling can reduce obesity. “It is not a sacrifice message,” she said. “It is trying to find ways to live a good life in a way that leaves a good atmosphere for the planet. I’ve found it really positive to make many of these changes.”

The researchers analysed dozens of sources from Europe, North America and Japan to calculate the carbon savings individuals in richer nations can make. They found getting rid of a car saved 2.4 tonnes a year, avoiding a return transatlantic flight saved 1.6 tonnes and becoming vegetarian saved 0.8 tonnes a year.

These actions saved the same carbon whichever country an individual lived in, but others varied. The savings from switching to an electric car depend on how green electricity generation is, meaning big savings can be made in Australia but the savings in Belgium are six times lower. Switching your home energy supplier to a green energy company also varied, depending on whether the green energy displaces fossil fuel energy or not.

Nicholas said the low-impact actions, such as recycling, were still worth doing: “All of those are good things to do. But they are more of a beginning than an end. They are certainly not sufficient to tackle the scale of the climate challenge that we face.”

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The researchers found that government advice in the US, Canada, EU and Australia rarely mentioned the high impact actions, with only the EU citing eating less meat and only Australia citing living without a car. None mentioned having one fewer child. In an analysis of school textbooks on Canada only 4% of the recommendations were high impact.

Chris Goodall, an author on low carbon living and energy, said: “The paper usefully reminds us what matters in the fight against global warming. But in some ways it will just reinforce the suspicion of the political right that the threat of climate change is simply a cover for reducing people’s freedom to live as they want.

“Population reduction would probably reduce carbon emissions but we have many other tools for getting global warming under control,” he said. “Perhaps more importantly, cutting the number of people on the planet will take hundreds of years. Emissions reduction needs to start now.”